The preparation of sustained release dosage forms which utilize water miscible drugs as substrates have long been plagued by problems. One major problem has been the tendency of such drugs to "dump" or "surge" into the body during the first hour or two after an oral dosage form containing them is swallowed. The problem is caused by their affinity for aqueous environments.
In the present invention certain readily water soluble drugs are administered in unique slow-or substained-release oral, vaginal, or rectal dosage forms. These dosage forms comprise a novel two-part system, a core or inner portion in which the drug is dispersed in a matrix of a water soluble polymer and an outer portion, which is a semi-permeable membrane containing a solvent. The solvent is a water-based polymeric coating solution. The solubility of the polymeric component is pH dependent.
U.S. Pat. Nos. 4,369,172 and 4,389,393 show the use of hydroxypropyl-methylcellulose and another celluloic material in a carrier base for a dosage form.
U.S. Pat. No. 4,443,428 describes oral dosage forms which contain a wax matrix. British application 2,068,226A shows sustained release compositions containing disopyramide, glyceryl monostearate, castor sugar, polyvinyl pyrrolidine, magnesium stearate, and a coating of hydroxypropylmethyl cellulose, glucose, and propylene glycol.